1. Field of the Invention
The present invention relates to a matching apparatus capable of matching input and output impedances between a power amplifying circuit and an antenna (load) for use in a portable wireless telephone set.
2. Description of the Related Art
Heretofore, official gazette of Japanese laid-open patent application No. 10-163889 has disclosed an automatic impedance matching system for automatically matching input and output impedances between a power amplifier and a load such as an antenna of a portable wireless telephone set.
FIG. 8 shows a matching apparatus capable of matching the power amplifier and the load disclosed in the above official gazette.
As shown in FIG. 8, a load impedance (including a matching circuit) detector 2 is provided between a power amplifier 1 and an antenna (load) 4, and a matching circuit 3 is controlled by a detection signal. The load impedance detector 2 detects the impedance as an R (resistance) and a "PHgr" (phase) respectively, and the detection signal is converted in the form of analog-to-digital signal by an A/D converter 5 and inputted to a microcomputer (CPU) 8. The CPU 8 drives a drive circuit 7 such as a motor or a relay and controls the matching circuit 3 in such a manner that the values of the R and the "PHgr" of the detection signal may be matched to the output impedance of the power amplifier 1.
The load impedance detector 2 is correctly adjusted in such a manner that a detection signal voltage of a load impedance becomes equal to a central value of a detection voltage under the state that input and output impedances obtained when the output impedance of the power amplifier 1 and the load impedance are matched with each other are 50xcexa9 (pure resistance). For example, the load impedance detector is correctly adjusted such that a detection voltage obtained when the input and output impedances are 50xcexa9 is set to 0 V, when the resistance R is larger than 50xcexa9, a positive voltage proportional to the R value may be detected, and when the resistance R is lower than 50xcexa9, a negative voltage which is inversely proportional to the R value may be detected. Further, the phase "PHgr" also is correctly adjusted in such a manner that positive and negative voltages from a central value may be detected in proportion to the phase value similarly.
The load impedance detector 2 thus correctly adjusted is used and the resistance R and the phase "PHgr" of the detection signal are inputted to the CPU 8. The CPU 8 variably controls the matching circuit 3 by driving the motor or relay drive circuit 7 in such a manner that the resistance R may constantly become equal to the corrected value of the impedance 50xcexa9 by decreasing the resistance R with a positive voltage signal proportional to the resistance R or by increasing the resistance R with a negative voltage. Accordingly, the output impedance of the power amplifier 1 and the load side impedance can be matched at 50xcexa9. The matching of the phase "PHgr" also can be controlled similarly.
With the above arrangement, when the output impedance of the power amplifier 1 is not matched to 50xcexa9, since the matching circuit 3 is controlled such that matching is conducted at 50xcexa9, the power amplifier 1 and the antenna 4 are not matched with each other completely and thereby displaced from each other. In particular, as the amplified band of the power amplifier 1 is increasing its width, the output impedance of the power amplifier 1 is changed depending upon frequency characteristics and hence the displacement of the aforesaid matching becomes remarkable.
In order to solve the above problem, the CPU 8 for controlling the matching circuit 3 by using a matching control program has the arrangement such that an impedance judgment threshold value in the matching control program can be changed in response to transmission frequencies by a judgment threshold value setting device 9.
According to the above arrangement, since the impedance judgment threshold value of the CPU 8 which control the matching circuit by the detection output is changed by an impedance changing means in response to the change of the output impedance of the power amplifier 1, when the output impedance of the power amplifier 1 is changed in response to the transmission frequency, even though the output impedance of the power amplifier 1 is displaced from the adjusted value by changing the impedance judgment threshold value with the transmission frequency the input and output impedances can reliably be matched with each other.
There arises a problem that the above conventional matching method needs the complex detector and various ICs such as the load impedance detector, the A/D converter, the motor relay drive circuit and the judgment threshold value setting device.
Further, in the above matching circuit, the impedance of the matching circuit is switched and compensated such that the output impedance in the power amplifier corresponds to the frequency. Specifically, although the frequency characteristic of the power amplifier receives an attention, in recent years, in a portable wireless telephone set and the like, there is executed a transmission power control (Transmission Power Control: hereinafter referred to as a TCP) which controls transmission power of a mobile station in such a manner that receiving power at the base station becomes the same in order to solve a near-far problem (near-far Problem) in a code division multiple access (Code Division Multiple Access: CDMA) or the like which receives an attention.
In the portable wireless telephone set of the terminal side in which such TCP is executed, an output efficiency of the power amplifier is not so excellent, and this output efficiency should be improved at the sacrifice of a stability. Accordingly, the stability is given a priority and the output efficiency is sacrificed.
Even when the output efficiency of the power amplifier is improved and the impedance is matched (matching) with the load at the maximum output power of the power amplifier in which the TPC, for example, is carried out, an output efficiency is extremely lowered at the portion in which the output power of the power amplifier is lowered as will be described later on.
The present invention is made in order to solve the above problem and the problem to be solved by the present invention is to provide a matching apparatus in which a matching circuit is switched and controlled in response to output power of a power amplifier without sacrificing both an output efficiency and a stability of the power amplifier.
According to the first invention, there is provided a matching apparatus which comprises a power amplifying means for transmitting output power based on a command for instructing an output, a matching means 2 connected between this power amplifying means 1 and a load 4 and a switching means 10 for switching input and output impedances of the matching means 2 based on a command for instructing the output power.
According to the second invention, in the matching apparatus according to the first invention, the switching means 10 is switched in multiple stages in response to a magnitude of output power from the power amplifying means 1.
According to the third invention, in the matching apparatus according to the first or second invention, when maximum output power is outputted from an output end of the power amplifying means 1, matching is conducted with the matching means 2 and when power is decreased from the maximum output power to predetermined output power, there is outputted a switching signal for switching the input and output impedances in which the matching means 2 is matched to the decreased predetermined output power.
According to the first invention to the third invention, the input and output impedances of the matching circuit are switched based on the output power instructing command from the base station and the like, whereby the detector can be constructed with ease. Therefore, there can be obtained the matching circuit in which the output efficiency and the stability are both satisfactory at the maximum output power and the small output power.